Multiple mode switching regulator having an automatic sensor circuit for power reduction

ABSTRACT

A switching regulator having a control circuit that automatically senses when a low power mode should be initiated without the use of expensive external components nor an extensive amount of external components is disclosed herein. The switching regulator includes an input switching device, a driver, an inductor, a first output switching device, a second output switching device and an output node. The control circuit includes a low power switching device connected to the output node and the second end of the inductor. An amplifier connects the low power switching device and the first output switching device. A first current mirror couples to the amplifier to mirror the difference between the output current through the output load and the current supplied at the second end of the inductor. A second current mirror couples to the first current mirror to mirror the current difference through a current source and a capacitor connected in parallel across the current source. A comparator compares the voltage generated by the capacitor with a predetermined voltage source. A first and second AND gate couples to the comparator. The output of the first AND gate provides a entry signal that initiates the low power mode for the switching regulator. The second AND gate couples to receive this entry signal. The output of the first AND gate provides a exit signal that indicates when the switching regulator is not in low power mode. The first AND gate couples to receive this exit signal.

FIELD OF THE INVENTION

The present invention relates to switching regulators, and, more particularly, to a multiple-mode switching regulator having an automatic sensor circuit that places the switching regulator in a low power mode.

BACKGROUND OF THE INVENTION

Switching regulators are used to provide a constant supply of voltage to the circuitry within prescribed voltage tolerances. They are often used in portable electronic devices that have lower power requirements where the input voltage is supplied by a power source, such as a battery, that may fluctuate overtime due to contact corrosion, dissipation, temperature or other external environment conditions or changes thereof. The switching regulator receives the input voltage from the power source and converts it to a voltage within the prescribed voltage tolerance. Thereby, the switching regulator provides a regulated output voltage to a load from an unregulated input voltage. Specifically, the switching regulator provides and maintains a predetermined output voltage to a portable electronic device circuitry coupled thereto. As such, circuitry incorporated within the switching regulator regulates the voltage to within prescribed voltage tolerances of the device circuitry even in the presence of wide deviations in the power source voltage.

The switching regulator may be used to convert a power source signal to a higher or lower controlled voltage output. A control circuit for generating pulse width modulation within the switching regulator functions as an oscillator which provides a periodic carrier signal. By rapidly opening and closing a switch within the switching regulator, the control circuit controls the average power that is provided to a load coupled to the switching regulator by controlling the average voltage applied to the load.

A typical switching regulator has at least two switches that switch ON and OFF out of phase with each other to supply current to a load. Three types of switching regulators include: buck mode switching regulators, which regulate an output voltage that is lower than the input voltage; boost mode regulators, which regulate an output voltage that is higher than the input voltage; and buck-boost mode switching regulators, which regulate an output voltage that is higher, lower, or the same as the input voltage. These three modes can be combined to form a multiple mode switching regulator.

A typical multiple mode switching regulator includes an inductor with a first end coupled to both a first high side switch, a first low side switch, and a second end coupled to both a second high side switch and a second low side switch. The first high side switch and first low side switch are on the input side. The second high side switch and second low side switch are on the output side. In buck mode, the first high side switch and first low side switch are switched ON and OFF out of phase with each other. In boost mode, the second high side switch and second low side switch are switched ON and OFF out of phase with each other. In buck-boost mode, the first high side switch and the second low side switch are switched ON and OFF in phase with each other, and the second high side switch and the first low side switch are switched ON and OFF in phase with each other, but out of phase with the first high side switch and second low side switch.

Advantageously, switching regulators are often used in electronic devices because of their greatly increased efficiency at higher loads. This increase in efficiency presents a substantial advantage for battery powered devices. The efficiency, however, is reduced greatly when a minimal current load is present. As a solution, a switching regulator may include a low power mode to increase the efficiency when the load current has fallen below a certain predetermined threshold. During the low power mode, various blocks within the regulator are turned off and a simpler control loop may be employed. Unfortunately, the simpler control loop decreases regulation tolerance.

Most switching regulators do not implement a low power mode that maintains a supply of regulated output voltage. Many switching regulators that include a low power mode do not automatically sense the output current in an effort to make a determination of whether the low power mode should be entered or exited from. Furthermore, many of these switching regulators require a low power mode input signal to initiate the low power mode. There, however, are a few switching regulators that sense the output current and provide a feature of automatic entrance and exit from a low power mode. Unfortunately, these switching regulators require an expensive precision resistor or a current transformer to sense current.

Thus, a need exists for a switching regulator having a low power mode that automatically senses when this mode should be initiated without the use of expensive external components nor an extensive amount of external components.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of switching regulators, the present invention teaches a switching regulator having a low power control circuit that automatically senses when the low power mode should be initiated without the use of expensive external components nor an extensive amount of external components. The switching regulator in accordance with the present invention includes a driver coupled to receive a first high side reference voltage. An input switching device includes a control node that connects to the driver and a drain node that receives an input voltage. A diode couples between the source node of the input switching device and ground. A first end of an inductor connects to the node formed between the source node of the input switching device and the diode. A first output switching device includes a drain node connected to the second end of the inductor and a control node connected to a high side output node. A second output switching device includes a drain node connected to the second end of the inductor and a control node connected to a low side output node. An output load connects to the source nodes of the first and second output switching devices. A low power control circuit couples across the inductor to monitors the current across the output load and automatically initiate the low power mode of the switching regulator independent of the value of the output load and the input voltage.

The low power control circuit includes a low power switching device that includes a control node connected to the high side output node and a drain node connected to the second end of the inductor. An amplifier connects to the source node of the low power switching device and the first output switching device. A first current mirror couples to the amplifier to mirror the difference between the output current through the output load and the current supplied at the second end of the inductor. A second current mirror couples to the first current mirror to mirror the current difference through a current source and a capacitor connected in parallel across the current source. A comparator compares the voltage generated by the capacitor with a predetermined voltage source. A first and second AND gate couples to the comparator. A first and second counter couple to the first and second AND gates respectively. The output of the first counter supplies a low power mode entry signal that initiates the low power mode for the switching regulator. The second AND gate couples to receive this low power mode entry signal. The output of the second counter supplies a low power mode exit signal that indicates when the switching regulator is not in low power mode. The first AND gate couples to receive this low power mode exit signal.

Advantages of this design include but are not limited to a switching regulator that automatically enters into a low power mode without the requirement of an external signal. The switching regulator in accordance with the present invention does not require an expensive precision resistor coupled to the output to sense output current; nor does it require an additional feedback pin from the resistor. This embodiment does implement the use of an additional capacitor; yet, this capacitor can be a standard ceramic type with no special requirements. In addition, the capacitor's value can vary widely without altering the performance of the switching regulator. This embodiment is also independent of input voltage, duty cycle, and most importantly output capacitance.

These and other features and advantages of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein:

FIG. 1 illustrates a known switching regulator;

FIG. 2 illustrates a switching regulator in accordance with the present invention;

FIGS. 3 displays the timing diagram of the switching node, the output current, the output voltage, the low power capacitance node, and the low power mode signal of the switching regulator shown in FIG. 2 for entrance and exit from the low power mode;

FIGS. 4 shows the timing diagram of the switching node, the output current, the output voltage, the low power capacitance node, and the low power mode signal of the switching regulator shown in FIG. 2 for entrance into the low power mode; and

FIG. 5 displays the timing diagram of the switching node, the output current, the output voltage, the low power capacitance node, and the low power mode signal of the switching regulator shown in FIG. 2 for exiting out of the low power mode.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set for the herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

The present invention is best understood by comparison with the prior art. Hence, this detailed description begins with a discussion of known switching regulator shown in FIG. 1 and the switching regulator disclosed in U.S. Pat. No. 6,650,100B1 entitled “Bootstrap Technique For A Multiple Mode Switching Regulator” which is incorporated herein.

FIG. 1 illustrates a known switching regulator 10 that includes a circuit driver D₁, an input switching device T₁, a diode D₀, an inductor L₁, a first output switching device T₃, a second output switching device T₂, an output capacitor C_(out1), and an output resistive load R_(load1).

As stated previously, a typical multiple mode switching regulator includes an inductor with a first end coupled to both a first high side switch, a first low side switch, and a second end coupled to both a second high side switch and a second low side switch. The first high side switch and first low side switch are on the input side. The second high side switch and second low side switch are on the output side. In buck mode, the first high side switch and first low side switch are switched ON and OFF out of phase with each other. In boost mode, the second high side switch and second low side switch are switched ON and OFF out of phase with each other. In buck-boost mode, the first high side switch and the second low side switch are switched ON and OFF in phase with each other, and the second high side switch and the first low side switch are switched ON and OFF in phase with each other, but out of phase with the first high side switch and second low side switch.

This circuit shown in FIG. 1, however, differs in design from the conventional switching regulator disclosed previously in that there is only one high side input switch T₁, whereas diode D₀ performs the function of the first low side input switch.

As shown, an input voltage V_(in1) is supplied to the drain node of input switching device T₁. The circuit driver D₁, connects to receive a high side input HSL₁. The output of circuit driver D₁, connects to the control node of input switching device T₁. The inductor L₁ couples between the source of the input switching device T₁ and the drain of the second output switching device T₂, while the source of second output switching device T₂ couples to ground. The drain of the first output switching device T₃ couples to inductor L₁. A high side output HSL₂ coupled to the control node of the first output switching device T₃, while a low side output LSL₁ couples to the control node of the second output switching device T₂. Capacitor C_(out1) and resistor R_(load1) couple in parallel across the source node of first output switching device T₃ and ground.

In operation, during buck mode, the input switching device T₁ is switched ON and OFF, while second output switching device T₂ is off completely and first output switching device T₃ is always on. When the input switching device T₁ turns off, node A₁ decreases to a voltage corresponding to diode D₀ below ground (−0.7V). The current builds in inductor L₁ because the current for the driver D₁ is higher than the output voltage, V_(out).

In boost mode, the first output switching device T₃ and the second output switching device T₂ are switched ON and OFF out of phase with each other.

In buck-boost mode, the input switching device T₁ and the second output switching device T₂ are switched ON and OFF in phase with each other, and the first output switching device T₃ is switched ON and OFF out of phase with the input switching device T₁ and second output switching device T₂.

As shown in FIG. 2, a switching regulator 100 in accordance with the present invention includes a circuit driver D₂, an input switching device T₄, a diode D₃, an inductor L₂, a first output switching device T₆, a second output switching device T₅, an output capacitor C_(out2) an output resistive load R_(load2), and low power control circuit 50. Low power control circuit includes a switching device T₇, an amplifier 10, a first current mirror 30, a second current mirror 32, a current source I₁, a capacitor C₁, a comparator 20, a first AND gate 22, a second AND gate 24, a first counter 26, and a second counter 28.

Switching regulator 100 uses an external capacitor C_(out2) and the internal sense FETs, T₆ and T₇, to determine the load current under any condition. Once the load current is sensed, the control circuit 50 within switching regulator 100 generates to signal that initiates entry into the low power mode LP_(enter) or exit therefrom LP_(exit). In addition, the switching device T₇ in the present invention is a sense FET. Conventional switching regulators do not use a sense FET as a second high side switching device as switching device T₇ has been implemented in this design. Most conventional switching regulators are designed to implement the use of an external sense resistor or a transformer.

As shown, an input voltage V_(in2) is supplied to the drain node of input switching device T₄. The circuit driver D₂ connects to receive a high side input HSL₃. The output of circuit driver D₂ connects to the control node of input switching device T₄. The inductor L₂ couples between the source of the input switching device T₄ and the drain of the second output switching device T₅, while the source of second output switching device T₅ couples to ground. The drain of the first output switching device T₆ couples to inductor L₂. A high side output HSL₄ coupled to the control node of the first output switching device T₆, while a low side output LSL₂ couples to the control node of the second output switching device T₅. Capacitor C_(out2) and resistor R_(load2) couple in parallel across the source node of first output switching device T₆ and ground.

Low power control circuit 50 includes sense switching device T₇ which connects to amplifier 10. Specifically, the drain node of sense switching device T₇ connects to the second end of inductor L₂, the control node couples to the high side output HSL₄, the source node couples to amplifier 10. Sense FET T₇ senses current in both the normal operating mode and the low power mode. Those skilled in the art may recognize that sense FET T₇ may be replaced with a similar switching device. Once the load current is sensed, given the value of capacitor C₁ is known, the average output current can be derived, even without continuous current through the FET T₆.

Current mirror 30 couples between amplifier 10 and second current mirror 32. Current mirror 32 connects to current source I₁. Capacitor C₁ couples across current source I₁. Sensing FET T₆ senses the current when the switching regulator goes into low power mode. Sense FET T₇ integrates the current with that processed through sense FET T₆. The resultant signal is amplified and mirrored into capacitor C₁. Current i₂ pulls a constant current out of capacitor C₁, while sense FET T₆ adds current i₁ into the capacitor C₁.

Comparator 20 couples to receive a voltage that is twice the value of the reference voltage V_(ref) and the voltage at node C_(LP). Effectively, comparator C₁ compares the voltage generated by the capacitor with this predetermined voltage. A first and second AND gate, 22 and 24, couples to comparator C₁. A first and second counter, 26 and 28, couple to the first and second AND gates, 22 and 24, respectively. The output of the first counter 26 supplies a low power mode entry signal LP_(enter) that initiates the low power mode for the switching regulator 100. The second AND gate 24 couples to receive this low power mode entry signal LP_(enter). The output of the second counter 28 supplies a low power mode exit signal LP_(exit) that indicates when the switching regulator 100 is not in low power mode. The first AND gate 22 couples to receive this low power mode exit signal LP_(exit).

Specifically, comparator 20 compares the voltage across current source 11 with the value of two times the reference voltage V_(ref). As shown, current i₁ is the current that enters node C_(LP) and current i₂ is the current provided by current source I₁. When current i₁ becomes less than current i₂, comparator 20 will generate a signal LP_(enter) that signifies that switching regulator 100 may enter low power mode, wherein signal LP_(enter) will be “high”. Counter 26 is a five bit counter that determines that switching regulator 100 will enter into low power mode after the signal is available over 32 cycles.

Switching regulator 100 functions as the following during the normal mode of operation. During buck mode, the input switching device T₄ is switched ON and OFF, while second output switching device T₅ is off completely and first output switching device T₆ is always on. When the input switching device T₄ turns off, node A decreases to a voltage corresponding to diode D₀ below ground (−0.7V). The current builds in inductor L₂ because the current for the driver D₁ is higher than the output voltage, V_(out).

Switching device T₄ turns on for a short period of time. The load current is discontinuous. It is only constant during the on period of the switch T₄. When switching device T₄ on, it integrates current into the capacitor C₁ through current i₁.

When switching device T₄ is high, switching device T₆ is on. Thereby, current flows through the inductor L₁ which produces a triangle wave. At the same time, switching device T₇ is on and senses the load current. Amplifier 10 mirrors the difference between the current sensed by sense switching device, T₇ and T₆, using current mirror 30 implemented by transistors, 12 and 14. The current through current mirror 30 is further mirrored by current mirror 32 implemented by 16 and 18 to provide current i₁ which is proportional to the load current.

During the determination of whether the switching regulator 100 should enter the enter low power mode, it is assumed that the voltage on the C_(LP) pin is above twice the reference voltage V_(ref), since it is pulled high during the startup of the device. In any of the operating modes, the average output amplifier and the external capacitor. If the average current is less than the current of the trimmed current source I₂, the voltage at node C_(LP) will start to decrease. Once the voltage drops below twice the reference voltage V_(ref), the comparator signals the LPModeSignal which goes into a 5-bit up counter. If 32 consecutive LPMode signals are received, then the part enters low power mode. This works for all modes, buck, boost, and buck-boost, since the average output current is always delivered through the T₄ FET. An example of entering low power mode is shown in FIG. 4.

Regarding exiting low power mode, most of the control loop circuitry and switching of the main power FETs are turned off until needed when the switching regulator is in low power mode. The switching frequency is then dependent upon the output load R_(load2) and the output capacitance C_(out2) with a hysteric operation determined by the comparators of the output voltage. When this is occurring, the current through switching device T₆ is discontinuous, with the output current supplied by the charge on the large output capacitor C_(out2). To sense output current during this case, a ratio of the output charge placed on the output capacitor C_(out2) is placed on capacitor C₁ and slowly bled off by a fixed internal current source I₁. If the charge placed on capacitor C₁ is less than the fixed internal sources time/current relationship, then the output current is less than the threshold, and switching regulator 100 stays in low power mode. If the charge increases above the internal current source threshold for two consecutive cycles, switching regulator 100 exits low power mode and runs at the standard fixed switching frequency.

Specifically, when current i₁ becomes greater than current i₂, comparator 20 will generate a signal that signifies that the switching regulator may exit low power mode. Counter 28 is a two bit counter that determines if the charge increases above the internal current source threshold for at least two consecutive cycles. When the charge is above the internal current source threshold for at least two consecutive cycles, the switching regulator 100 exits low power mode and runs at the standard fixed switching frequency. An example of this operation is shown in FIG. 5.

In boost mode and buck-boost mode, switching regulator will function similar to that of buck mode with the following exceptions. Specifically, in boost mode, the first output switching device T₆ and the second output switching device T₅ are switched ON and OFF out of phase with each other. In buck-boost mode, the input switching device T₄ and the second output switching device T₅ are switched ON and OFF in phase with each other, and the first output switching device T₆ is switched ON and OFF out of phase with the input switching device T₄ and second output switching device T₅.

If node C_(LP) is pulled low through an external source, such as a microprocessor, the part will go into low power mode after 32 cycles have elapsed. When pulled high, it will exit low power mode after two cycles. The currents of the sources are low enough, on the order of tens of micro amps, that the external source is not required to be strong to overdrive the control currents.

Those of skill in the art will recognize that the physical location of the elements illustrated in FIG. 2 can be moved or relocated while retaining the function described above. For example, diode D₃ may be implemented with a low side input switching device coupled to a driver, wherein the driver couples to a low side input node.

Furthermore, those skilled in the art will recognize that counters, 26 and 28, merely provide a “wait state” for the switching regulator, wherein the switching regulator waits for a predetermined amount of time after having received low power condition prior to entry into the low power mode. Thereby, an alternate embodiment may remove counters, 26 and 28, and still provide a switching regulator having a control circuit that automatically determines when the switching regulator should enter and exit low power mode.

FIG. 3 displays the timing diagram of the switching node, the output current, the output voltage, the low power capacitance node, and the low power mode signal of the switching regulator shown in FIG. 2 for entrance and exit from the low power mode. As shown when the switching regulator is in low power mode and the output current increases above a particular threshold, the switching regulator exits low power mode.

FIG. 4 illustrates a timing diagram of specific signals and nodes of the switching regulator just prior to entry into a low power mode and after entry into a low power mode. As shown, switching node A₂ switches from −1 volt to 9 volts. Although hard to distinguish with the naked eye, the output current and voltage decrease as time increases. The voltage at node C_(LP) consistently decreases as well. When the output voltage reaches the threshold of being less than twice the reference voltage V_(ref), then the low power mode signal is generated as shown. This signals duration lasts for 32 cycles and then the switching regulator enters into low power mode.

FIG. 5 displays the timing diagram of the switching node, the output current, the output voltage, the low power capacitance node, and the low power mode signal of the switching regulator shown in FIG. 2 for exiting out of the low power mode. As shown in FIG. 5, when the switching device T₄ is on, as indicated by switching node A₂, the voltage at node C_(LP) rises. This is a direct result of the increase of current i₁. When switching device T₄ turns off, the voltage at node C_(LP) decreases in value since current i₂ subtracts from that which is supplied at node C_(LP).

Advantages of this design include but are not limited to a switching regulator having a control circuit that automatically determines when the switching regulator will enter or exit a low power mode without the requirement for an external signal. It does not require an expensive precision resistor on the output to sense output current, as well as an additional feedback pin from the resistor. It does require an additional capacitor, however, this capacitor can be a standard ceramic type with no special requirements. It's value can vary widely and the system will still work correctly. It is also independent of input voltage, duty cycle, and most importantly output capacitance.

Since entrance and exit from the low power mode occurs automatically with a separate external capacitor C₁ that is independent from the output capacitor C_(out2) nor the input voltage, this circuit will work with any value of an output capacitor or any input voltage without affecting the point where the switching regulator exits or enters the low power mode. Most known switching regulators point of entry or exit into and out of the low power mode, however, are effected by the value of the external capacitor or output voltage. For example, if the external capacitor is altered, the current required for the switching regulator to enter or exit the low power mode will be changed. Furthermore, in conventional switching regulators, if the voltage of the input driver changes, the point that the switching regulator enters or exits low power mode will change.

The reader's attention is directed to all papers and documents which are filed concurrently with this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All the features disclosed in this specification (including any accompany claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow. 

1. A switching regulator, comprising: a driver coupled to receive a first high side control signal; an input switching device having a source node, a drain node, and a control node, the control node coupled to an output of the driver, the drain node coupled to receive an input voltage; a diode coupled between the source node of the input switching device and ground; an inductor having a first end coupled to the source node of the input switching device; a first output switching device having a drain node coupled to the second end of the inductor, the first output switching device having a control node coupled to a second high side control signal; a second output switching device having a drain node coupled to the second end of the inductor, the second output switching device having a control node coupled to a low side control signal, the second output switching device having a source node coupled to ground; an output load coupled between the source nodes of the first and second output switching devices; an output capacitor coupled between the source nodes of the first and second output switching devices to provide an output voltage; and a low power control circuit coupled across the inductor, wherein the low power control circuit monitors the current delivered to the output load and automatically initiates the low power mode of the switching regulator independent of the value of the output voltage, the output capacitor, the inductor and the input voltage.
 2. A switching regulator as recited in claim 1, wherein the low power control circuit comprises: a low power switching device having a control node coupled to receive the high side control signal and a drain node coupled to the second end of the inductor; an amplifier coupled to the source node of the low power switching device and the first output switching device; a first current mirror coupled to the amplifier to mirror the output current delivered to the output load through the low power switching device; a second current mirror coupled to the first current mirror; a current source coupled between the second current mirror and ground; a capacitor coupled across the current source; a comparator coupled to the second current mirror and coupled to receive a predetermined voltage source to compare the voltage across the capacitor with the predetermined voltage source; a first AND gate coupled to the comparator and to receive the low power mode signal; an inverter coupled to receive the low power mode signal to generate an inverted low power mode signal; a second AND gate coupled to the comparator and to receive the inverted low power mode signal and the inductive switch signal; a first counter, having an input and an output, the input coupled to the first AND gate to provide a low power entry signal at the output, the output coupled to the second AND gate; and a second counter, having an input and an output, the input coupled to the second AND gate to provide a low power exit signal at the output, the output coupled to the first AND gate.
 3. The switching regulator as recited in claim 1, wherein the first input switching device is a transistor.
 4. The switching regulator as recited in claim 1, wherein the second input switching device is a transistor.
 5. The switching regulator as recited in claim 1, wherein the first output switching device is a transistor.
 6. The switching regulator as recited in claim 1, wherein the second output switching device is a transistor.
 7. The switching regulator as recited in claim 1, wherein the first input switching device is a metal-oxide-semiconductor field-effect transistor (Mos FET).
 8. The switching regulator as recited in claim 1, wherein the second input switching device is a Mos FET transistor.
 9. The switching regulator as recited in claim 1, wherein the first output switching device is a Mos FET transistor.
 10. The switching regulator as recited in claim 1, wherein the second output switching device is a Mos FET transistor.
 11. The switching regulator as recited in claim 1, wherein the output load is a resistor.
 12. The switching regulator as recited in claim 2, wherein the low power switching device is a transistor.
 13. The switching regulator as recited in claim 2, wherein the low power switching device is a sense FET transistor.
 14. The switching regulator as recited in claim 2, wherein the first current mirror, comprises: a first transistor, having a drain node coupled to the source node of the low power switching device; and a second transistor coupled to the first transistor, the control node of the first and second transistors coupled to the amplifier, the source node of the second transistor coupled to the source node of the first transistor.
 15. The switching regulator as recited in claim 2, wherein the second current mirror, comprises: a first transistor, having a drain node, a source node, and a control node, the drain node coupled to the control node and the drain node coupled to the first current mirror; and a second transistor having a drain node, a control node and a source node, the control node coupled to the control node of the first transistor, the source node coupled to the source node of the first transistor, the drain node coupled to the capacitor. 